The invention relates to automated fluid analysis. More particularly, but not exclusively, the invention relates to techniques for obtaining the concentration of a chemical in liquid across a widely varying concentration range, and in particular the level of dithionite in groundwater during a remedial soil treatment procedure.
Monitoring the levels of particular soil or groundwater constituents is a matter of great concern, and many techniques exist for measuring these concentrations when they remain within a relatively narrow range. However, there are some applications where the concentration of a particular soil constituent is expected to vary across several orders of magnitude. In these situations, it is more difficult and time consuming to obtain accurate data by conventional methods.
For example, soil contamination is often remediated by applying a second chemical into or around the contaminated site. This second chemical, can have beneficial effects by reacting with and decomposing the soil contaminates and/or by forming a barrier to prevent the further spread of the soil contamination. However, this second chemical is sometimes applied in large quantity to a central well and allowed to diffuse or otherwise migrate through the soil. Accordingly, the level of the applied chemical and/or the reaction byproducts at any point in time will likely vary substantially throughout the site depending upon, for example, the distance from the injection well, the local soil conditions, and reaction rate. Knowledge of these time and spacial dependent chemical levels is plainly important in determining the extent and effectiveness of the remediation operation. While groundwater samples can be relatively easily obtained from a group of monitoring wells throughout the site, conventional analysis techniques limit the speed and reliability at which these groundwater samples can be analyzed. Accordingly, conventional analysis techniques limit the ability to have real time knowledge about the remediation process.
One particular remediation method involves the injection of dithionite into the soil and is more fully described in U.S. Pat. No. 5,783,088 to Amonette, the disclosure of which is incorporated by reference. In addition to the problems of widely varying concentrations, dithionite is known to decompose when exposed to oxygen in air or an aqueous environment. This chemical instability necessitates special handling, such as maintaining the sample in an oxygen free environment, further complicating the task of quickly and reliably obtaining an accurate concentration measurement.
One dithionite analysis system has been developed by the present inventors that makes some progress toward meeting this need in the art, but further developments are needed. The present system provides a measured groundwater sample from a sample loop to a syringe pump assembly. There, the sample is diluted with degassed water and injected into a flow through detector. However, the dilution range of this device is limited in that only a single sample size can be provided to the mixing chamber. If the dilution achieved with that single sample size in inadequate, the sample loop must be removed and replaced or manual dilution must be performed. Each of these alternatives is time consuming and undesirable. Accordingly a need exists for a system that can provide multiple dilutions across a widely varying range for rapid and accurate fluid analysis.
In addition, the present device does not provide fully automated undiluted analysis of the groundwater sample. If a diluted groundwater sample is too dilute to produce a useful absorbance signal, an operator must recognize this inadequacy, switch programs, and directly provide the sample to a separate injection port. This too is a complicated process leading to operator error or the simple failure to obtain the data. Especially where numerous samples from multiple wells must be run, a system that can automatically perform direct analysis of a groundwater sample in addition to diluted analysis is needed.
These and other needs are satisfies by various embodiments of the present invention.
In one aspect the invention comprises a novel fluid analysis system for performing automated fluid analysis over a widely varying concentration range.
In another aspect the invention provides a novel fluid analysis system for performing automated groundwater analysis during a remediation injection. In one aspect the remedial chemical is dithionite.
In one embodiment there is provided a method for monitoring levels of soil chemicals following a remediation injection, comprising: providing a groundwater sample to an apparatus comprising a sample injection assembly operatively coupled to a controller, the injection assembly adapted to selectively provide one of at least two dissimilar predetermined volumes of a fluid sample to a mixing assembly in response to signals received from the controller, the injection assembly including a multiport injection value and at least two sample loops of dissimilar volume, selecting one of the at least two dissimilar predetermined volumes of the fluid sample, transferring the selected volume of the fluid sample to the mixing assembly in response to a signal from the controller, transferring a predetermined volume of dilution fluid to the mixing assembly, mixing the predetermined volumes of dilution fluid and fluid sample to create a first diluted fluid sample, performing a concentration measurement on the first diluted sample. The method can also include selecting a second one of the at least two dissimilar predetermined volumes of the fluid sample, transferring the second selected volume of the fluid sample to the mixing assembly, transferring a second predetermined volume of dilution fluid to the mixing assembly, mixing the second predetermined volumes of dilution fluid and the second selected volume of fluid sample to create a second diluted fluid sample, performing a concentration measurement on the second diluted sample. The method can also include transferring a third selected predetermined volume of fluid to the mixing assembly and performing a concentration measurement on the third fluid sample.
In another embodiment there is provided a novel method for monitoring levels of soil chemicals following a remediation injection, comprising: providing a groundwater sample to an apparatus comprising a sample injection assembly operatively coupled to a controller, the injection assembly adapted to automatically provide one of at least two dissimilar predetermined volumes of a fluid sample to a mixing assembly in response to signals received from the controller, the injection assembly including a multiport valve in fluid communication with at least one sample loop, the injection assembly further including a sample inlet port able to be placed in fluid communication with the multiport valve and the mixing chamber, selecting one of the at least two dissimilar predetermined volumes of the fluid sample, transferring the selected volume of the fluid sample to the mixing assembly in response to a signal from the controller, transferring the fluid from the mixing assembly to a flow through detector to perform a concentration measurement on the fluid.
There is also provided a novel groundwater sampling device comprising: a controller; a mixing assembly for receiving a groundwater sample and a predetermined volume of a dilution fluid in response to signals from the controller; a flow through detector in fluid communication with the mixing assembly for determining the concentration of a component of the groundwater sample; and an injection assembly in fluid communication with the mixing assembly and a source of baseline fluid, the injection assembly adapted to selectively provide one of at least two dissimilar predetermined volumes of the groundwater sample to the mixing assembly in response to signals received from the controller, the injection assembly including a multiport injection value and at least two sample loops of dissimilar volume in fluid communication with the multiport injection valve, wherein at least two distinct dilutions of the groundwater sample can be automatically provided to the flow through detector for concentration measurements.
There is also provided an automated fluid analysis system comprising: a controller; a mixing assembly for receiving a fluid sample and a predetermined volume of a dilution fluid to form first and second diluted fluid sample, the mixing assembly adapted to form the diluted fluid samples and provide them to a detector for analysis in response to signals from the controller; and an injection assembly in fluid communication with the mixing assembly and a source of dilution fluid, the injection assembly adapted to selectively provide one of at least two dissimilar predetermined volumes of the fluid sample to the mixing assembly in response to signals received from the controller, the injection assembly including a multiport injection value and at least two sample loops of dissimilar volume in fluid communication with the multiport injection valve, the mixing assembly including a multi port selector valve coupled to a syringe pump, the multi port selector valve operable to place the syringe pump in fluid communication with the injection assembly, a second syringe member, and the detector in response to signals from the controller, wherein at least first and second diluted fluid samples can be automatically provided to the detector for analysis in response to signals from the controller.